In order to increase the transmission capacity of optical fiber networks and communication links, wavelength division multiplexing (WDM) techniques are often utilized. In WDM systems, a plurality of wavelength channels is transmitted through a single optical fiber. Fibers are connected at points known as “nodes”, at which channels are rerouted towards their final destinations via the best possible fiber paths. Channels may also be added or dropped at so called add/drop points. Generally, at the nodes the WDM-signal is demultiplexed, the individual signals re-routed and sent down the chosen fiber, possibly multiplexed into another WDM signal. At add/drop points, spectrally selective optical switches, also known as channel drop filters, are utilized for extraction of a single wavelength channel from a WDM signal, or for insertion of a single wavelength channel into a WDM signal.
The network may be designed to be either static or re-configurable. A re-configurable network is essential to provide provision of wavelengths and enable protection switching. In a re-configurable network, the nodes and/or add/drop points are equipped with switches or dynamic wavelength converters, giving it the capability to change the routing pattern.
A technology used to enable optical rerouting are MEMS switches, which utilizes small moveable mirrors displaceable to dispatch the optical signal to the chosen fiber. Such an optical switch is presented in U.S. Pat. No. 6,292,281, in which a matrix of mirrors are provided on a silicon wafer based structure. Also, the nodes may be provided with add-drop filters designed to add or drop a specific chosen channel to or from the WDM channel.
However, the prior art technology suffers from several drawbacks. Optical MEMS switches are complicated and difficult to manufacture, and are devices that require de-multiplexing and multiplexing of the WDM signal.
Therefore, there is a need for devices and methods for coupling individual channels within a WDM signal from one fiber to another enabling an easily re-configurable and dynamic network.